MICA: Determining the therapeutic potential of targeting mTORC-1/2 in chronic lymphocytic leukaemia - a pre-clinical study

Chronic lymphocytic leukaemia (CLL) is the most common blood cancer in the UK and is currently incurable with chemotherapy. Of the 3000 new diagnoses/year, two thirds of patients will eventually require treatment, and while the majority of these patients initially respond to current first-line chemotherapy, all eventually relapse due to the re-emergence of leukaemic cells that evaded initial treatment. There is no defined second-line treatment plan for relapsed patients, highlighting the unmet medical need for additional therapeutic options in CLL

It is now accepted that the leukaemic B cells in CLL interact with several types of supportive cells within patient lymphoid organs (lymph nodes and bone marrow); these cells provide survival and growth signals to the leukaemic cells, and several studies demonstrate that these associations prevent currently used chemotherapy agents from delivering maximal effect in the patient. We hypothesise that one particular protein called mTor, which is commonly deregulated in other human cancers, plays a central role in regulating key proteins responsible for maintaining CLL cell protection and survival and promotes disease progression. Indeed, our preliminary data support this hypothesis, establishing that mTor is active both in primary CLL cells derived from the blood or lymph node, and cells derived from a CLL mouse model. Moreover we establish that mTor is further activated when CLL cells are exposed to microenvironmental signals present in the lymphoid organs. Our investigations indicate that further studies analysing the role of mTor in CLL cell survival and proliferation are warranted, as it may represent a promising drug target in CLL.

We have developed powerful experimental approaches involving the in vitro culture of human CLL cells in nurturing microenvironments that replicate the signals received in patient lymph nodes, and CLL mouse models that closely replicate advanced human disease in vivo. With these model systems we will elucidate the role of mTor in maintenance and progression of CLL and explore avenues for therapeutic inhibition of mTor-mediated signals, using highly selective mTor inhibitors that have already been tested in the clinic for solid tumour malignancies. Therefore we will:
1 - Examine the impact of inhibiting mTor on CLL cell survival and proliferation;
2 - Define whether mTor is active in lymphoid organs derived from CLL patients;
3 - Determine how mTor inhibition, using selective inhibitors, influences disease progression in CLL mouse models in vivo.
Collectively, the proposed studies will establish whether mTor inhibition represents a valid drug target in CLL, gaining valuable information that could inform the design of future clinical trials in CLL. Moreover, a fundamental understanding of the role played by mTor in regulating CLL cell proliferation and survival may assist in the discovery of novel protein markers (biomarkers) that will enable clinicians to stratify patients into subgroups, identifying those patients that would respond well to mTor-targeted therapies, both in CLL and other cancer types.

Chronic lymphocytic leukaemia (CLL) is refractory to current chemotherapeutic regimes, highlighting the need for novel therapies. Recent research has established that in addition to cellular accumulation due to increased expression of anti-apoptotic proteins, CLL cells also exhibit enhanced proliferation within patient lymph nodes (LN), promoting disease progression. Targeting survival and proliferation signals represent a promising way to deliver a curative strategy for CLL. The protein kinase mammalian target for rapamycin (mTor) forms two distinct complexes mTorc-1 and mTorc-2, which promote cell survival and proliferation. Our preliminary data demonstrate that mTorc-1 and -2 substrates are activated both in ex vivo and proliferating human primary CLL cells, and in cells derived from a CLL mouse model. While the mTorc-1 inhibitor rapamycin inhibits CLL proliferation, it is not cytotoxic to CLL cells, leading us to hypothesise that dual targeting of mTorc-1/2 will preferentially disrupt proliferation/survival pathways present in CLL patient LN microenvironment to induce apoptosis. To delineate the functional and molecular roles played by mTorc-1/2, we will utilise three complementary experimental systems:
- Primary CLL LN tissue biopsies, to determine the activation status of mTorc-1/2 in a biologically-relevant setting in vivo;
- CLL samples cultured in in vitro experimental systems that mimic in vivo survival- or proliferative signals, to assess the impact of manipulating mTor signalling with shRNA techniques or dual mTorc-1/2 inhibitors;
- CLL mouse models, to assess the therapeutic response of mTor inhibition in vivo.
These model systems will enable us to define the importance of mTor as a valid therapeutic target for CLL. Moreover, elucidating the molecular signatures that accompany mTor inhibition in CLL cells may lead to the identification of potentially novel biomarkers, which will assist in future clinical trial design.

Patients diagnosed with chronic lymphocytic leukaemia (CLL) frequently become refractory to current first-line immunochemotherapeutic regimes. Those who are not transplant candidates have few therapeutic options, highlighting the need for novel therapeutic options. The key aim of the proposed pre-clinical study is to establish whether mTor inhibition represents a new and valid therapeutic target in chronic lymphocytic leukaemia (CLL), utilising a potent and selective dual mTorc-1/2 inhibitor, AZD8055. CLL represents a novel disease area for AZD8055, which has already been tested in the clinic in solid malignancies, and the proposed study will generate valuable information that will assist in future design of clinical trials. Furthermore, as part of this study we aim to generate data leading to the discovery of novel biomarkers to assist clinicians in the stratification of patient cohorts, identifying subgroups that will respond to mTor-targeted therapies either alone or in combination, both in CLL and other cancer types. The ultimate goal of our research will be the delivery of quality adjusted life years for patients, through the amelioration of disease; achieved with appropriate use of targeted therapies.

The key beneficiaries of the proposed research will be:
- Commercial private sector (pharmaceutical and diagnostic companies) will benefit (within 5 years) from both newly discovered biomarkers and potential new drug targets to enable positioning of their research programmes into appropriate disease areas and in the development of prognostic and diagnostic kits;
- Key opinion leaders and physicians within the field of oncology will benefit (5 - 7 years) as it will enable them to suggest/promote optimised regimens or drive forward stratification of patients into clinical trials;
- Clinical trial organisations will benefit through trials of novel drugs and combinations of therapeutics (5 - 7 years);
- Patients will benefit (7 - 10 years) from appropriately tailored clinical trial design;
- Health organisations and policy makers (such as NHS, National Institute for Clinical Excellence) will benefit (7 - 10 years) from a novel prognostic biomarker as it will enhance the focus of health resources towards more appropriate targeted therapies to responsive groups, permitting the deployment of NHS resources towards other clinical areas.

Therefore the identification and exploitation of novel prognostic biomarkers will provide a global leadership position in oncology, benefiting our industrial partner, AstraZeneca. Exploiting these outputs will enable AstraZeneca to consider novel disease indications for mTorc-1/2 inhibitors, and allow targeting to more focused drug-responder subgroups. By extension, benefit will also be gained by other companies that exploit parallel IP by discovering novel pharmacophores, small-molecules or similar.